Among check valves for preventing backflow of fluid, there is one that comprises a casing having a fluid passage, a valve seat member disposed in the fluid passage, and a valve element closing the fluid passage by sealingly abutting against a valve seat surface of the valve seat member in the fluid passage. For example, Patent Literature 1 discloses a check valve wherein the valve element is urged so as to be pressed against the valve seat surface by a spring, and when a fluid pressure applied to the valve element in the forward direction exceeds the urging force of the spring, the valve element is displaced downstream to open the fluid passage, whereas when a fluid pressure is applied to the valve element in the reverse direction, the valve element is pressed against the valve seat surface by the urging force of the spring and the fluid pressure to maintain a state where the fluid passage is closed. In check valves used for fluid of relatively low pressure, a seal ring formed by an elastic member such as rubber is interposed between the valve element and the valve seat surface to seal between the valve element and the valve seat surface. Check valves used for high-pressure fluid involve the possibility that the seal ring may be broken by the high-pressure fluid, and are therefore often configured to close the fluid passage by a metal-to-metal sealing structure in which a valve element and valve seat member which are formed of a metal or other material of high rigidity are abutted directly against each other, as in the check valve of Patent Literature 1. To ensure high sealing performance with the metal-to-metal sealing structure, it is demanded that the valve seat surface and an abutting portion of the valve element that is to abut against the valve seat surface should be machined with high accuracy.